As a technique for controlling a legged mobile robot such as a bipedal walking robot, there has been generally known so-called position control proposed in, for example, Patent Document 1 by the applicant of the present application. According to the disclosed technique, the target displacement amount of each joint of a robot is sequentially determined on the basis of a target motion of the robot (e.g., the trajectory of a target position of the distal end of a leg of the robot), and then the actuator of each joint is drivably controlled so as to cause an actual displacement amount to coincide with the target displacement amount.
According to the position control described above, the actual displacement amount of a joint is maintained to be constant as long as the target displacement amount of the joint remains constant, thus presenting poor flexibility in response to a change in an external force acting on the robot.
As a solution to the inflexibility, there has been known a technique disclosed in, for example, Patent Document 2. According to the technique, a spring member is interposed between a joint and an actuator to impart flexibility to the joint, and a target driving force for each joint to accomplish a target motion of a robot is determined by inverse dynamics calculation so as to control the actual driving force of each joint to the target driving force thereof by so-called force control.